What should i do (farewell party tomorrow?)?

As long as you don't make a habit of it, what's wrong with being a bit bad every now and then? Sneak the clothes out with you and change somewhere. Its your leaving party so its how you will be remembered. Wear what you want just this one time, you'll feel good and you will have more fun at the party and will remember it in a much better way. HAVE A GREAT NIGHT AND GOOD LUCK WITH COLLEGE!